A. Field of Invention
The present invention pertains generally to measuring and testing devices and more particularly to in-circuit test devices for testing digital components.
B. Description of the Background
Quality control of manufacturing and production require implementation of systems for testing electronic components after they have been physically soldered onto printed circuit boards.
Several different approaches have been used for testing components. For example, functional testing uses a procedure of applying predetermined input signals and monitoring the output of the printed circuit board to determine if all of the components are present and operating properly. Although funtional testing provides an excellent way of determining, as an end result, whether the PC board is functioning properly, it provides little or no information with regard to analysis of the functioning of individual components on the board. Complex programming techniques have been used to provide limited information as to the location of non-functioning components on the board by carefully selecting input data and analyzing the output data. Such systems are complex, often costly to implement and normally provide vague information as to the location of malfunctioning components.
Because of the limitations of functional testing, in circuit testing techniques have been used that individually test the components on the board to determine if they are working properly. In this manner, non-functioning components can be readily identified and replaced to prevent the entire circuit board from being scrapped.
Another class of testing devices that provides simpler tests and is less expensive to implement are the manufacturing defect analyzers which are designed to locate manufacturing faults such as shorts on a PC board, missing IC's, bent component pins, etc. Although these devices do a reasonable job of finding shorts and gross analog faults, they are marginal when testing digital sections of the board. Hence, a need exists for a device which is capable of performing the functions of a manufacturing defects analyzer to determine if a digital component is present and properly connected to the circuit. It is also desirable to provide, in conjunction with such a test, a method of providing transfer tests of the digital components.